Tokkai Hei 8-340663 published by the Japanese Patent Office in 1996 discloses a motor/generator wherein two rotors and one stator are arranged coaixally in three layers. When one of the rotors is used as a motor, the other is used as a generator. In this motor/generator, two sets of coils are installed in the stator for providing a magnetic field for respective rotors, and two sets of inverters, i.e., current controllers, are provided, for controlling respective sets of coils.